JPH0969665A - Semiconductor light emitting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a more easily usable light emitting device by suppressing the beam shape from degrading without losing the merits of an S<3> laser. SOLUTION: First and second current squeezing layers 31 and 27 are formed with a spacing on p-type clad layers 26, 28, 30, etc., located on the upper (or lower) part of an MQW active layer 25, and low-impurity concn. high-resistance layer 29 is inserted between these layers 31 and 27.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a beam shape, that is, a near field pattern.
The present invention relates to a semiconductor light emitting device useful as a visible light semiconductor laser having excellent n: NFP).

At present, as a semiconductor laser used for a light source of an optical disk or the like, the recording density increases as the wavelength of light becomes shorter, so that GaInP / oscillates in the visible light region.
AlGaInP-based materials are sought after.

In particular, in order to write on an optical disc, a visible light semiconductor laser having a high output and excellent beam characteristics is required, and the present invention can meet the demand.

The beam characteristics required for a semiconductor laser for an optical disk are astigmatism (shift of the focal position in the horizontal and vertical directions of the laser beam), the aspect ratio of the far field image (laser It means that the aspect ratio of the cross section of the beam is close to 1, that is, the laser beam is close to a perfect circle, and the near-field image is unimodal.

[0005]

2. Description of the Related Art Conventional materials that have reached a practical range as visible light semiconductor laser materials include GaInP ternary system and A
1GaInP quaternary material, a visible light semiconductor laser is manufactured using these materials, and the wavelength is 590 [nm].
It is possible to generate a laser beam of about 670 [nm].

However, in the above material system, it is difficult to re-grow crystals on the layer containing Al.
A buried structure cannot be formed.

Therefore, due to insufficient lateral confinement of the injected current, a ridge structure with a poor beam aspect ratio and large astigmatism is unavoidably adopted.

FIG. 2 is a fragmentary front view showing a visible light semiconductor laser having a ridge structure formed by a conventional technique.

In the figure, 1 is an n-GaAs substrate, 2 is an n-InGaAlP cladding layer, 3 is an InGaP active layer, 4 is a p-InGaAlP cladding layer, and 5 is n-Ga.
As current confinement layer, 6 is a p-GaAs contact layer, 7 is a p-side electrode, and 8 is an n-side electrode.

In order to solve the above-mentioned problem of the visible light semiconductor laser having the ridge structure, the present inventors have made S ³ (self-a).
Signed stepped substrate)
A visible light semiconductor laser called a laser was provided (see JP-A-4-250280, if necessary).

FIG. 3 is a fragmentary front view showing an S ³ laser which is a visible light semiconductor laser with improved lateral confinement of injected current.

In the figure, 11 is an n-type substrate, 12 is an n-type cladding layer, 13 is an active layer composed of three well layers and two barrier layers, 14 is a p-type cladding layer, and 15 is a lateral direction. N-type portion 15A, p-type portion 15B, and n-type portion 15C that are continuous
Is a current confinement layer, 16 is a p-type cladding layer, and 17 is a p-type contact layer.

The S ³ laser produces a bend in the active layer 13 by forming a laser structure on a substrate 11 having a step formed by etching, thereby making it a real refractive index waveguide type, and having a good aspect ratio and a low refractive index. Astigmatism is achieved.

Further, since the current confinement layer 15 is formed immediately above the active layer 13 by utilizing the plane orientation dependence of the doping, the threshold voltage is about half that of the ridge structure described with reference to FIG. The current density is obtained.

Furthermore, the structure shown in the figure can be produced by a single crystal growth step, which is effective for cost reduction.

[0016]

As described above,
The S ³ laser has many advantages, but the beam shape (N
It was found that FP) deteriorates.

FIG. 4 shows S ³ for explaining the flow of the injection current.
FIG. 4 is a cutaway front view of an essential part showing a laser, and the same symbols as those used in FIG. 3 represent the same parts or have the same meanings.

In the current confinement layer 15 shown in the figure, the width of the p-type portion 15B, that is, the stripe width is about 2 [μm], and the width of the p-side electrode 18 is 10 [μm]. Then it becomes extremely narrow.

Therefore, the current is strongly confined and the active layer 13
As shown in the current distribution in the active layer shown in the figure, the current density at both edge portions of the active layer 13 becomes higher than that at the central portion, resulting in deterioration of the beam shape. To do.

It can be considered that the problem that the current is strongly confined as described above does not occur if the p-side electrode 18 is formed on the same stripe as the p-type portion 15B without being formed on the entire surface.

However, in that case, since an electrode having a width of 2 μm, for example, is formed in a stepped portion, lithography is not easy, and not only a voltage is applied but also a considerable current is applied. Since it must be flowed, it is not preferable in terms of heat generation and heat dissipation of the electrodes.

The present invention intends to prevent deterioration of the beam shape and to make it easier to use without impairing the advantages of the S ³ laser.

[0023]

According to the present invention, although the number of semiconductor layers is slightly increased, the injection current to the S ³ laser is started to be narrowed away from the active layer, and the current is made uniform. Basically, it is made to flow into the active layer after being converted.

From the above, in the semiconductor light emitting device according to the present invention, (1) a barrier layer (for example, p-side cladding layers 26 and 28) above or below the active layer (for example, MQW active layer 25).
And 30) and the like and a first current confinement layer (for example, the first current confinement layer 31) and a second current confinement layer (for example, the second current confinement layer 27) that are formed at intervals from each other. Or

(2) In the above (1), a high resistance layer (for example, a low impurity concentration high resistance layer 29) is interposed between the first current confinement layer and the second current confinement layer. Is characterized by.

By adopting the above-mentioned means, the current injected from the electrode is laterally nonuniform in the vicinity of the first current confinement layer due to a sharp confinement, but this nonuniformity causes current diffusion. Is gradually relaxed, and the voltage drop is almost determined by the resistance by passing through the low-impurity-concentration and high-resistance layer, so that the current becomes uniform, and the second current confinement layer further reduces the active layer. The spread of the current immediately above is suppressed, and as a result, the deterioration of NFP due to the distribution of the current flowing through the active layer is eliminated.

The number of semiconductor layers is slightly increased in order to realize the above-mentioned action. However, including the increased semiconductor layers,
Similar to the conventional S ³ laser, it can be produced in a single crystal growth step, so there is no difficulty in its implementation, and low threshold current, good aspect ratio, low non- Since a good NFP can be realized while maintaining the advantages of the conventional S ³ laser such as point aberration, it is more than sufficient to compensate the disadvantage of a slight increase in the number of semiconductor layers.

FIG. 1 is a fragmentary front view showing a semiconductor light emitting device for explaining an embodiment of the present invention.

In the figure, 21 is a shaped substrate, 22 is a buffer layer, 23 is an intermediate layer, 24 is an n-side cladding layer, 25 is an MQW (multi quantum well) active layer, 26 is a p-side cladding layer, and 27 is An n-type portion 27A and a p-type portion 27B which are formed by simultaneous doping and are continuous in the lateral direction.
And a n-type portion 27C, a second current confinement layer 28, a p-side clad layer, 29 a low impurity concentration and high resistance layer, 30 a p-side clad layer, and 31 formed by simultaneous doping and connected in the lateral direction n. A first current confinement layer composed of a mold portion 31A, a p-type portion 31B and an n-type portion 31C, 32 is an intermediate layer, 3
3 is a contact layer, 34 is a p-side electrode, and 35 is an n-side electrode.

The following is an example of the main data regarding each of the above parts. (1) Regarding Shaped Substrate 1 Material: Surface index of n-GaAs main surface: (100) Surface index on slope of stepped portion: (411)

(2) Regarding the buffer layer 22 Material: n-GaAs Impurity: Si Impurity concentration: 1 × 10 ¹⁸ [cm ⁻³ ] Thickness: 0.5 μm

(3) Intermediate layer 23 Material: n-GaInP Impurity: Si Impurity concentration: 1 × 10 ¹⁸ [cm ⁻³ ] Thickness: 0.1 μm

(4) About n-side clad layer 24 Material: n- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P Impurity: Si Impurity concentration: 1 × 10 ¹⁸ [cm ^-3 ] Thickness: 2 [μm]

(5) About MQW active layer 25 Well layer Material: GaInP (eg Ga _0.5 In _0.5 P) Thickness: 6 [nm] Number of layers: 3 Barrier layer Material: (Al _0.4 Ga _0.6 ) _0.5 In _0.5 P thickness S: 5 [nm] Number of layers: 2

(6) P-side clad layer 26 Material: p- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P Impurity: Zn Impurity concentration: 1 × 10 ¹⁸ [cm ⁻³ ] Thickness: 0.2 [μm]

(7) Regarding the second current confinement layer 27 n-type portions 27A and 27C Material: n-AlGaInP Impurity: Se Impurity concentration: 4 × 10 ¹⁷ [cm ⁻³ ] Thickness: 0.2 [μm]

P-type portion 27B Material: p-AlGaInP Impurity: Zn Impurity concentration: 7 × 10 ¹⁷ [cm ^-3 ] Thickness: 0.2 [μm]

(8) P-side clad layer 28 Material: p- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P Impurity: Zn Impurity concentration: 1 × 10 ¹⁸ [cm ^-3 ] Thickness: 1 [μm]

(9) About low impurity concentration and high resistance layer 29 Material: p-AlGaInP Impurity: Zn Impurity concentration: 5 × 10 ¹⁶ [cm ⁻³ ] Thickness: 20 [nm]

(10) P-side clad layer 30 Material: p- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P Impurity: Zn Impurity concentration: 1 × 10 ¹⁸ [cm ⁻³ ] Thickness: 0.5 [μm]

(11) Regarding the first current confinement layer 31 n-type portions 31A and 31C Material: n-AlGaInP Impurity: Se Impurity concentration: 4 × 10 ¹⁷ [cm ^-3 ] Thickness: 0.2 [μm]

P-type part 31B Material: p-AlGaInP Impurity: Zn Impurity concentration: 7 × 10 ¹⁷ [cm ⁻³ ] Thickness: 0.2 [μm]

(12) About the intermediate layer 32 Material: p-GaInP Impurity: Zn Impurity concentration: 1 × 10 ¹⁸ [cm ^-3 ] Thickness: 0.1 [μm]

(13) Contact layer 33 Material: p-GaAs Impurity: Zn Impurity concentration: 1 × 10 ¹⁸ [cm ⁻³ ] Thickness: 0.1 μm

(14) P-side electrode 34 Material: Ti / Pt Thickness: 100 [nm] / 300 [nm]

(15) About n-side electrode 35 Material: AuGe Thickness: 300 [nm]

It is extremely easy to manufacture the semiconductor light emitting device described with reference to FIG. 1, and the process thereof will be described next.

(1) For example, metal organic chemical vapor deposition (meta)
organic vapor phase exit
axy: MOVPE) method, the buffer layer 22, the intermediate layer 23, the n-side cladding layer 24, the MQW active layer 25, the p-side cladding layer 26, the second current confinement layer 27 are formed on the shaped substrate 21. The p-side clad layer 28, the low impurity concentration and high resistance layer 29, the p-side clad layer 30, the first current confinement layer 31, the intermediate layer 32, and the contact layer 33 are grown.

(2) The p-side electrode 34 is formed on the contact layer 33 by applying, for example, a vacuum evaporation method.

(3) By applying a mechanical polishing method to which chemical means is added, the back surface of the shaped substrate 21 is polished to a thickness of, for example, about 150 [μm].

(4) The n-side electrode 35 is formed on the back surface of the polished shaped substrate 21 by applying, for example, a vacuum evaporation method.

(5) As a laser having a resonator having a length of 700 μm, the laser is cleaved in the direction perpendicular to the stripe,
Completed by making into chips.

In the above process, the first current confinement layer 31
In the case of growing the second current constriction layer 27 and Zn at the same time as Zn as a p-type impurity and Se as an n-type impurity, Zn is added to the sloped step portion whose surface index is (411) and Se. Are gathered in the main surface portion whose surface index is (100), the n-type portion
It is known that 7A, the p-type portion 27B, and the n-type portion 27C, and the laterally continuous n-type portion 31A, the p-type portion 31B, and the n-type portion 31C are generated spontaneously.

[0054]

In the semiconductor light emitting device according to the present invention, the first current confinement layer and the second current confinement layer are formed on the barrier layer above or below the active layer with a space therebetween. It

According to the above structure, the current injected from the electrode is laterally non-uniform in the vicinity of the first current confinement layer due to the rapid constriction. As it progresses toward the layer, it is gradually relaxed by diffusion, and by passing through the low-impurity-concentration high-resistance layer, the voltage drop is almost determined by the resistance, so that the current becomes uniform, and further, the second The current confinement layer suppresses the current spreading right above the active layer, and as a result, the deterioration of NFP due to the distribution of the current flowing through the active layer is eliminated.

In order to obtain the above-mentioned effect, the number of semiconductor layers is slightly increased, but the semiconductor layers including the increased number of semiconductor layers are all formed in one crystal growth step as in the conventional S ³ laser. Therefore, there is no difficulty in its implementation, and while maintaining the advantages of the conventional S ³ laser such as low threshold current, good aspect ratio and low astigmatism, it is good. Realization of a new NFP
This is more than enough to compensate for the disadvantage of increasing the number of semiconductor layers.

[Brief description of drawings]

FIG. 1 is a fragmentary front view showing a semiconductor light emitting device for explaining an embodiment of the present invention.

FIG. 2 is a fragmentary front view showing a visible light semiconductor laser having a ridge structure formed by a conventional technique.

FIG. 3 is a fragmentary front view showing an S ³ laser which is a visible light semiconductor laser in which lateral confinement of injected current is improved.

FIG. 4 is a fragmentary front view showing an S ³ laser for explaining a flow of an injection current.

[Explanation of symbols]

 21 shaped substrate 22 buffer layer 23 intermediate layer 24 n-side cladding layer 25 MQW active layer 26 p-side cladding layer 27 second current confinement layer 27A n-type portion 27B p-type portion 27C n-type portion 28 p-side cladding layer 29 low impurity High-concentration resistance layer 30 p-side clad layer 31 first current confinement layer 31A n-type portion 31B p-type portion 31C n-type portion 32 intermediate layer 33 contact layer 34 p-side electrode 35 n-side electrode

Claims (2)

[Claims] 1. A semiconductor light emitting device comprising a barrier layer above or below an active layer, and a first current confinement layer and a second current confinement layer formed at intervals from each other. . 2. The semiconductor light emitting device according to claim 1, wherein a high resistance layer is interposed between the first current confinement layer and the second current confinement layer.